ORIGINAL PAPER

Contrasting sedimentation rates in Lake Illawarra and StGeorges Basin, two large barrier estuaries on the southeastcoast of Australia

Craig R. Sloss • Brian G. Jones •

Brendan P. Brooke • Henk Heijnis •

Colin V. Murray-Wallace

Received: 16 April 2009 / Accepted: 4 February 2011 / Published online: 15 February 2011

� Springer Science+Business Media B.V. 2011

Abstract Sedimentation rates over the last 100

years within two lagoons on the southeast coast of

Australia, Lake Illawarra and St Georges Basin, have

been quantified to determine the effects of catchment

land use change and native vegetation clearance on

infill rates, and spatial variations in the rate at which

the estuaries have filled. Both catchments have

similar lake and catchment area but have experience

different degrees of modification due to land clearing

for agriculture practices, urbanisation and industri-

alisation. Results indicate that in the heavily modified

catchment of Lake Illawarra sedimentation rates

close to fluvial deltas can be in excess of 16 mm/

year, and between 2 and 4 mm/year in the adjacent

central basin. This is approximately an order of

magnitude greater than the pre-European rates. In

contrast, at St Georges Basin, where the catchment

has experienced much less modification, sedimenta-

tion rates in the central basin appear to have remained

close to those prior to European settlement. However,

sedimentation rates in the urbanized margin of St

Georges Basin are relatively high (up to 4.4 mm/

year). This rapid modern sedimentation in the margin

of the estuarine embayments has been detected in

several other estuaries in the region. However the

degree of sedimentation within the bay-head deltas,

and more significantly in the central basin appears

proportional to the degree clearance of native vege-

tation (forest) in the catchment, urban expansion and

development of heavy industry in the respective

catchment areas.

Keywords Lagoonal infilling � Delta progradation �Geochronology � Amino acid racemisation �Lead-210 � Cesium-137 � Landuse changes

Introduction

Estuaries are environmentally, economically and

recreationally very valuable coastal environments

(Costanza et al. 1997; Robinson 2001). Accordingly,

it is essential for their sustainable management to

understand how these systems respond to changing

land use patterns and environmental conditions.

C. R. Sloss (&)

The Discipline of Biogeoscience, Queensland University

of Technology, GPO Box 2434, Brisbane, QLD 4001,

Australia

e-mail: c.sloss@qut.edu.au

B. G. Jones � C. V. Murray-Wallace

School of Earth and Environmental Sciences, University

of Wollongong, Wollongong, NSW 2522, Australia

B. P. Brooke

Geoscience Australia, GPO Box 1666, Canberra,

ACT 2601, Australia

H. Heijnis

Australian Nuclear Science and Technology Organisation,

Menai, NSW, Australia

123

J Paleolimnol (2011) 46:561–577

DOI 10.1007/s10933-011-9507-z

Changes to these systems can be via natural processes

(e.g. sea-level fluctuations, inlet channel infilling and

migration, and natural sedimentation) or induced by

human modification such as increased sediment,

nutrient and contaminant loads associated with agri-

cultural practices, urbanisation and industrial devel-

opment (Brooke 2003). In this study, sedimentation

rates pre- and post-European settlement (i.e. \200

years) within the Lake Illawarra and St Georges

Basin barrier estuaries on the southeast coast of

Australia has been determined from sediment cores

using a combination of 210Pb and 137Cs profiles, plus

radiocarbon and aspartic acid racemisation-derived

ages on fossil molluscs within the sediment.

European settlement on the Illawarra region coast

commenced in the early 1800s. Since that time the

region has undergone rapid and extensive clearing for

agricultural, industrial and urban development, to the

point that the many coastal catchments are now

significantly modified landscapes (Chenhall et al.

1995, 1994, 2001, 2004; Hagan and Wells 1997;

Sloss et al. 2004a, b). Such land use modification has

altered the geomorphological characteristics and

sedimentation trends within the coastal catchments;

this is particularly evident in estuarine environments

which act as a sediment sink between the catchment

and the coast. These changes have often led to rapid

siltation and choking of navigation routes; increased

nutrient loads leading to proliferation of algal

blooms; and increased turbidity and loss of a range

of estuarine flora and fauna (Chenhall et al. 1995,

2004; Taylor et al. 2004). However, studies that

quantify sedimentation rates in estuarine environ-

ments on the southeast coast of Australia are lacking.

This study utilises a multi-proxy geochronological

investigation that quantifies sedimentation rates

following European settlement in both heavily and

moderately modified catchments.

Study sites

Lake Illawarra

Lake Illawarra, located approximately 80 km south

of Sydney (Fig. 1), fills a shallow (\30 m) incised

valley system scoured into the upper Permian Shoal-

haven Group by river action during previous low-

stands of sea-level (Roy and Peat 1975; Sloss et al.

2005, 2006). The estuarine lake is impounded by

Windang Peninsula, a coastal barrier, and is con-

nected to the ocean by a 1.4 km long inlet channel.

The back-barrier estuarine lake covers an area of

approximately 36 km2 and has a maximum water

depth of 3.2 m. Due to the coastal barrier and narrow

inlet channel, the average impounded water level is

approximately 0.24 m above Australian Height

Datum (AHD; equivalent to present mean sea level;

Umitsu et al. 2001; Sloss et al. 2007). The estuary is

elongate in a general northeast–southwest direction

with two river mouths along its western margin,

Mullet Creek in the northwest and Macquarie Rivulet

in the southwest.

Mullet Creek has a single fluvial channel and lobate

subaqueous fluvial delta up to 1 km wide that extends

0.6 km east-southeast from the mouth of the creek into

the Lake Illawarra (Fig. 2). As sediment load associ-

ated with stream discharge enters the estuarine water

body, the sandy sediments are reworked and moved

alongshore by internally generated wind and wave

currents, producing a characteristic wave-dominated

delta morphology. The fine-grained fraction that

remains in suspension is transported into the deeper

portions of the central receiving basin (Jones et al.

1976; Sloss et al. 2004a, b, 2005).

Macquarie Rivulet enters the lagoon in the south-

west in a relatively sheltered embayment with lower

wind and wave energy. Macquarie Rivulet has a

higher discharge than Mullet Creek and, as a result,

its delta is dominated by river flow. This has

produced a delta with bifurcating channels, and

distributary mouth bars (Sloss et al. 2005; Hopley

et al. 2007) and thin, lobate sub-deltas that have

created a classic birdsfoot delta morphology that

extends 1.3 km into the lagoon (Fig. 2). Together

Mullet Creek and Macquarie Rivulet, along with

numerous smaller streams, drain a combined catch-

ment area of approximately 332 km2.

St Georges Basin

St Georges Basin is a large bi-lobate wave-domi-

nated barrier estuary located 190 km south of

Sydney (Fig. 1). The estuary has infilled a broad

and shallow incised valley scoured into the ante-

cedent Pleistocene landsurface and mid Permian

sandstone and siltstone during periods of lower sea

level (Sloss et al. 2006). The estuary is impounded

562 J Paleolimnol (2011) 46:561–577

123

by the Bherwerre Barrier system that forms the

largest sand barrier complex in the region (Bradshaw

1987, 1993; Sloss et al. 2006; Fig. 3). The estuary

has a surface area of approximately 40 km2 with a

maximum water depth of approximately 10 m.

Wandandian Creek, the main river flowing into St

Georges Basin, has formed a substantial fluvial delta

at its entrance in the northwest corner of the lake

(Hopley and Jones 2006). The smaller Tomerong

Creek forms a fluvial delta that separates Erowal

Bay from the main basin in the northeast corner

(Fig. 3). These two creeks, together with numerous

smaller streams, drain a total catchment area of

approximately 400 km2, 80% of which remains

forested (Haese et al. 2007). The remainder of the

catchment is occupied by agriculture and rapidly

expanding urban areas, particularly in the Erowal

Bay region. The basin is connected to the Pacific

Ocean by a narrow sinuous inlet 6.3 km in length.

Due to the coastal sand barrier restricting open

ocean influences and the lengthy inlet channel the

tidal range within the basin is reduced to 3.5 cm

with an average impounded water body approxi-

mately 18 cm above AHD (Sloss et al. 2007).

South Pacific Ocean

NEW SOUTH WALES

SYDNEY

SYDNEY

35°S

34°S Blue

Mountains

Illawarra Escarpment

Continetal shelf margin

Eastern Highlands (200 m contour)

N.S.W.

WOLLONGONG

Lake Illawarra

St Georges Basin

Lake Conjola

N 20 km

Burrill Lake Tabourie Lake

Fig. 1 Map of the New South Wales southern coast showing the location of the estuaries investigated in this study

J Paleolimnol (2011) 46:561–577 563

123

Methods

Core collection and sediment analysis

Five push cores, two from Lake Illawarra and three

from St Georges Basin were collected for 210Pb

analysis of recent sediment. The push-cores were

obtained from various water depths in the central

basin mud facies and fluvial pro-deltas, with recov-

eries between 0.25 and 0.30 m (Table 1). Retrieved

cores were split and visually logged documenting

colour, sediment texture, lithological composition

and significant facies changes. A visual assessment of

the preservation and relative abundance of

macrofossil populations was made on all the cores

collected to provide an account of the faunal assem-

blages preserved in estuarine facies. The core logs

were adjusted for sediment compaction during core

collection (measured vs. recovered depth based on a

linear regression). Visual assessment was made of

any potential surface mixing, however for each of the

cores this was absent. Additional data to establish

pre-European sedimentation rates were obtained from

sedimentological and geochronological data derived

from longer vibracores reported in Sloss et al. (2005,

2006).

Approximately 1 gram of sediment was collected

every 0.5–1 cm from the push cores for sediment

VC38

LkPb2 VC4

LkPb1

Fluvial channel deposits

Back-swamp deposits

Subaerial exposed tidal Sand-flats

Subaqueous tidal sand-flats with abundant sea-grass

Muddy sand with moderate Sea-grass beds

Pro-delta sandy mud and silt

Estuarine silty mud

Core location

137Cs Core 500 m

Haywards Bay

Koona Bay

VC5

VC6

VC7

VC8

Mullet Creek

500 m

Hooka Creek

Tank Trap

Duck Creek

Hooka Creek

Mullet Creek

Macquarie Rivulet

Lake Illawarra: Fluvial bay-head deltas

VC14 VC15

VC13

VC3 VC2

VC1

MRD#3

MRD#2

LI41

(a)

(b)

(c)

Horsley Inlet

Fig. 2 Core locations and facies divisions within Lake Illawarra. For details on vibracores see Sloss et al. (2006)

564 J Paleolimnol (2011) 46:561–577

123

analysis and 210Pb dating. Sediment collected for

particle size analysis was disaggregated in water by

immersion in an ultrasonic bath. Sodium hexameta-

phosphate was added to prevent flocculation of the

fine-grained detritus. Samples were analysed using a

Malvern Mastersizer 2000 laser particle size analyser

to establish the sediment characteristics (\2 mm).

Lead-210 dating

Sediment samples were taken at 0.5 cm intervals,

dried at 50�C for 24 h then crushed into a fine powder

using a mortar and pestle. The crushed samples were

chemically processed using the standard methods

employed by the Environment Division Laboratories

at the Australian Nuclear Science and Technology

Organisation (ANSTO), Sydney (Haworth et al.

1999).

Sediment accumulation rates and sample age esti-

mates based on the measured 210Pb activities were

calculated using the Constant Initial Concentration

(CIC) model (Krishnaswamy et al. 1971; Haworth et al.

1999). The CIC model assumes that at each stage of

sediment accumulation the initial concentration of

unsupported 210Pb is constant regardless of bulk

sediment accumulation (Krishnaswamy et al. 1971;

Fluvial channel deposits

Subaerial exposed tidal Sand-flats

Subaqueous tidal sand-flats with abundant sea-grass

Bhewerre Barrier

5 km

Worrowin Waterway

Tomerong Creek

Erowal Bay

6113

6112

6111

285 286

EbPb2

EbPb1

StPb1

Muddy sand with moderate sea-grass beds

Estuarine silty mud

Vibracore location

210Pb Core location

Fig. 3 Core locations and

facies divisions within St

Georges Basin. For details

on vibracores see Sloss

et al. (2006)

Table 1 Details of cores collected for 210Pb analysis

Code Geographic location UTM easting UTM northing Water depth (cm) Core depth (cm)

LkPb1 Lake Illawarra: Macquarie Rivulet pro-delta 299250 6175062 320 29

LkPb2 Lake Illawarra central basin 302038 6179033 320 29

StPb1 St Georges Basin: Outside Erowal Bay 285520 6111713 300 25

EbPb1 St Georges Basin: Erowal Bay 285450 6113670 80 30

EbPb2 St Georges Basin: Erowal Bay 285402 6113306 80 30

J Paleolimnol (2011) 46:561–577 565

123

Haworth et al. 1999). No independent markers were

available to assess the performance of the CIC model

(sensu Smith 2001). However, the linear nature of the210Pb profiles render this the most suitable model.

Since 210Pb decays logarithmically with time from its

initial activity, with a decay constant of 0.03114 per

year, the sediment age at any depth is given by:

tz ¼ ð1=kÞlogeðA0=AÞ;

where tz is the age at depth z; k is the 210Pb decay

constant; A0 is the initial unsupported 210Pb activity

per unit mass; and A is the unsupported 210Pb activity

per unit mass at depth z (Haworth et al. 1999).

The 210Po and excess 210Pb data from alpha

spectrometric counting of the sediment samples for

each core are presented in Table 2 and Fig. 4. Also,

Table 2 Geochemical data for cores analysed for 210Pb

Core Depth

(cm)

ANSTO

laboratory code

Activity of

Po-210 (Bq/kg)

Activity of

Ra-226 (Bq/kg)

Activity of excess210Pb (Bq/kg)

LkPb1 0–0.5 G380 48.8 ± 1.1 8.7 ± 0.6 40.1 ± 1.2

1–1.5 G381 58.7 ± 1.4 6.5 ± 0.4 52.1 ± 1.4

2–2.5 G382 48.0 ± 1.2 9.2 ± 0.6 38.8 ± 1.3

4.5–5 G383 53.4 ± 1.3 7.3 ± 0.5 46.1 ± 1.4

5.5–6 G384 24.3 ± 1.1 8.7 ± 0.7 15.6 ± 1.3

12–12.5 G385 52.2 ± 2.0 6.4 ± 0.5 45.7 ± 2.1

16–16.5 G386 17.8 ± 0.9 8.1 ± 0.6 9.7 ± 1.1

LkPb2 0–0.5 G174 54.8 ± 1.7 6.5 ± 0.4 48.3 ± 1.7

3.5–4 G175 46.3 ± 1.5 4.6 ± 0.4 41.7 ± 1.5

5–5.5 G176 44.0 ± 1.5 6.4 ± 0.4 37.6 ± 1.5

6.5–7 G177 43.0 ± 1.4 7.1 ± 0.5 35.9 ± 1.5

9–9.5 G393 40.3 ± 1.6 7.8 ± 0.7 32.5 ± 1.8

11.5–12 G178 35.6 ± 1.0 5.5 ± 0.4 30.2 ± 1.1

22–22.5 G394 15.9 ± 0.7 8.0 ± 0.8 7.9 ± 1.5

27–27.5 G179 12.5 ± 0.5 5.5 ± 0.4 7.0 ± 0.6

StPb1 0–1 G167 54.3 ± 2.1 3.0 ± 0.2 51.3 ± 2.1

2.5–3 G168 37.6 ± 1.0 1.9 ± 0.2 35.6 ± 1.0

5–5.5 G169 29.2 ± 1.2 2.5 ± 0.2 26.7 ± 1.2

8–8.5 G170 18.6 ± 0.6 2.4 ± 0.2 16.2 ± 0.7

12–12.5 G171 12.6 ± 0.5 8.1 ± 0.5 4.5 ± 0.7

20–20.5 G173 9.0 ± 0.4 4.2 ± 0.3 4.8 ± 0.5

EbPb1 0.75 ± 0.25 D313 94.6 ± 3.1 3.0 ± 0.3 91.6 ± 3.1

4.75 ± 0.25 D314 106.8 ± 3.3 3.7 ± 0.3 103.1 ± 3.3

9.75 ± 0.25 D315 84.3 ± 3.4 2.2 ± 0.2 82.1 ± 3.4

19.5 ± 0.5 D316 38.3 ± 2.1 2.1 ± 0.1 36.3 ± 2.1

29.5 ± 0.5 D317 20.6 ± 0.8 1.9 ± 0.1 18.7 ± 0.8

EbPb2 5.25 ± 0.25 D895 63.7 ± 1.7 2.5 ± 0.2 61.2 ± 1.7

9.75 ± 0.25 D896 41.9 ± 1.8 2.4 ± 0.2 39.5 ± 1.769

15.5 ± 0.5 D897 10.3 ± 0.3 2.3 ± 0.2 8.0 ± 0.4

20.5 ± 0.5 D898 3.7 ± 0.2 1.4 ± 0.1 2.3 ± 0.2

30.5 ± 0.5 D899 5.2 ± 0.2 2.8 ± 0.2 2.5 ± 0.3

Fig. 4 Plot of the geochemical data showing excess 210Pb

activity plotted against core depth and age depth plot of the

normalised 210Pb against core depth using the CIC mode

respectively for: LkPb2 (a, b), StGBPb (c, d), EbPb1 (e, f), and

EbPb2 (g, h)

c

566 J Paleolimnol (2011) 46:561–577

123

LkPb2: Plot of excess Pb-210 Activity (Bq/kg) vs Depth

0

5

10

15

20

25

30

00.00100.0100.1

Dep

th (

cm)

excess Pb-210 activity (Bq/kg)Age (years) based on the CIC Model

0

2

4

6

8

10

12

14

-5 0 5 10 15 20

Dep

th (

cm)

Age (years)

(a)

(c)

(b)

StGBPb: Plot of excess Pb-210 Activity vs Depth

0

5

10

15

20

25

0.01 0.10 1.00 10.00 100.00

Pb-210 (excess) Activity (Bq/kg)

Dep

th (

cm)

Age (years) based on the CIC Model

0

0.5

1

1.5

2

2.5

3

3.5

4

-10 0 10 20 30 40 50 60 70 80

Age (years)

Dep

th (

cm)

(d)

(e) (f)

0

5

10

15

20

25

30

35

1 10 100 1000

Pb-210 activity (Bq/Kg)

Dep

th (

cm)

EbPb1: Plot of excess Pb-210 activity vs depth Age (years) based on the CIC Model

0

5

10

15

20

25

30

35

0 20 40 60 80

Age (years)

Dep

th (

cm)

EbPb2: Plot of excess Pb-210 activity vs depth

0

5

10

15

20

25

30

35

001011

Pb-210 activity (Bq/Kg)

Dep

th (

cm)

Age (years) based on the CIC Model

0

5

10

15

20

25

0 50 100 150 200

Age (years)

Dep

th (

cm)

(g) (h)

J Paleolimnol (2011) 46:561–577 567

123

226Ra data, which gives an indication of sediment

source, are presented in Table 2. The excess 210Pb

activities have been normalised using the measured

\62.5 lm grain size fraction of each 210Pb sample

(Haworth et al. 1999). Age-depth profiles were

calculated for each of the cores (Fig. 4).

Cesium-137

In the southern hemisphere the first detectable appear-

ance of this anthropogenic radionuclide is identified in

sediment profiles from 1955 (Leslie and Hancock

2008). Its distribution in sedimentary cores can exhibit

two maxima at ca 1958 and 1963 (Livens and Rimmer

1988; Walling and He 1992, 1997; Leslie and Hancock

2008). Samples were chemically processed using the

methods employed by the Environment Division

Laboratories at ANSTO (Haworth et al. 1999).

Amino acid racemisation

Amino acid racemisation is a biochemical dating

technique that is based on the chemical changes that

occur in proteins within carbonate shell following the

death of the organisms. Some of these chemical

changes are time-dependent and can provide the basis

for a chronological control based on the ratio of

levorotatory enantiomers that rotate plane-polarised

light to the left (exclusively utilized during life) and

dextrorotatory enantiomers (rotating plane-polarised

light to the right). This ratio (the D/L ratio) is

determined by the rate of racemisation of L enantio-

mers to the corresponding D enantiomers upon death

of an organism (Miller and Hare 1980; Miller and

Brigham-Grette 1989; Wehmiller and Miller 2000).

Aspartic acid, one of the fastest racemising amino

acids, is utilized to derive numeric ages over time

scales of decades to centuries (Goodfriend 1991,

1992; Goodfriend and Stanley 1996). This is an

interval of time that is difficult to date by more

established methods. 210Pb, for example, is applicable

only for the past 150 years and 14C dating of marine

shells may not uniquely define ages within the past

500 years when conventional radiocarbon ages are

expressed in sidereal years (i.e. the possibility of

multiple potential ages for one radiocarbon measure-

ment). Sloss et al. (2004b) highlighted the potential

for the aspartic acid dating method to ‘‘fill the gap’’

between radiocarbon and 210Pb dating.

In this study, the extent of aspartic acid racemi-

sation in the fossil molluscs Anadara trapezia,

Notospisula trigonella and Batillaria australis that

are commonly preserved in estuarine successions in

southeastern Australia have been used to establish

sedimentation rates for pre- and post-European

settlement (Sloss et al. 2005; Table 3). Sample

preparation and analytical techniques undertaken for

this study follow the procedures outlined in Murray-

Wallace and Kimber (1987), Murray-Wallace (1993)

and Sloss et al. (2004b, 2006). Average aspartic acid

D/L ratios for each sample analysed were based on at

least three replicate injections on a Hewlett-Packard

model 5890A series II Gas Chromatograph at the

Amino Acid Dating Laboratory, University of

Wollongong, Australia. Additional aspartic acid rac-

emisation derived ages have been determined by

re-calculating previously published results from Sloss

et al. (2005) using more precise calibration curves

(Sloss et al. 2006).

Radiocarbon age determinations

In this study five specimens of B. australis were dated

to provide a framework in which to assess the aspartic

acid racemisation rate in the epifauna gastropod (time

series experiment; Figs. 6, 7). AMS radiocarbon ages

were obtained from the Australian Nuclear Science and

Technology Organisation (ANSTO), Sydney, NSW.

The total radiocarbon dataset and their sources are

summarised in Table 5. Radiocarbon ages were cali-

brated to sidereal years using the radiocarbon calibra-

tion program CALIBTM REV5.0.1 (Stuiver and

Reimer 1993; Stuiver et al. 1998a, b). Calibration for

fossil molluscs used the marine model calibration

curve (Marine04) with a Dr value of 11 ± 85 year to

correct for the marine reservoir effect and convert ages

into sidereal years (expressed as cal year BP; Gillespie

1977; Gillespie and Polach 1979; Stuiver et al. 1998a,

b; Table 6).

Dating results

Lead-210

210Pb age-depth profiles were calculated for four of

the short cores (LkPb2, StGBPb1, EbPb1 and EbPb2;

Fig. 4). Each of these cores exhibited relatively

568 J Paleolimnol (2011) 46:561–577

123

constant sedimentation rates. Based a visual assess-

ment of each core and the 210Pb profile there is

minimal surface mixing (Table 2; Fig. 4). In contrast

core LkPb1 collected from the pro-delta region of the

Macquarie Rivulet delta in the southwestern limb of

the Lake Illawarra estuary exhibits significant

reworking (Fig. 2). Based on changes in activity of

excess 210Pb with depth, results from this core

suggest that the sediment profile for at least the top

30 cm experienced reworking. Sediment mixing to

depths of 30 cm is most likely due to a combination

of bioturbation, the interaction of wind-generated

currents and hydrodynamic characteristics of Mac-

quarie Rivulet. Accordingly, it was not possible to

estimate sample ages from the excess 210Pb activities.

Lake Illawarra: central basin (LkPb2)

This core was collected from the central receiving

basin of the Lake Illawarra estuary, representing a

Table 3 Aspartic acid racemisation-derived ages on N. trigonella from estuaries on the NSW southern coast

Core

code

UTM

easting

UTM

Northing

Sample UWGA

laboratory code

Sample core

depth (cm)

Average aspartic

acid D/L ratio

Aspartic acid

derived age

Cumulative

sedimentation rate

(mm/year)

Facies

code

LkPb1 299506 6175199 UWGA-1441 10 0.095 ± 0.006 100 ± 5 1.0 CBM

LkPb1 UWGA-1442 13 0.121 ± 0.002 250 ± 10 0.5 CBM

LkPb1 UWGA-1443 14 0.124 ± 0.001 270 ± 10 0.5 CBM

LkPb1 UWGA-1445 28 0.145 ± 0.002 450 ± 20 0.6 CBM

LkPb1 UWGA-1446 29 0.161 ± 0.002 610 ± 30 0.5 CBM

LkPb2 302038 6179033 UWGA-1418 9 0.078 ± 0.003 40 ± 5 2.3 CBM

LkPb2 UWGA-1419 18 0.136 ± 0.007 360 ± 20 0.5 CBM

LkPb2 UWGA-1420 19 0.142 ± 0.002 410 ± 20 0.5 CBM

LkPb2 UWGA-1421 23 0.161 ± 0.001 590 ± 30 0.4 CBM

LkPb2 UWGA-1422 26 0.167 ± 0.001 650 ± 30 0.4 CBM

VC3a 301800 6180250 UWGA-772 65 0.113 ± 0.003 190 ± 10 3.4 CBM

VC4a 302100 6179000 UWGA-1109 18 0.080 ± 0.001 40 ± 5 4.5 CBM

VC4a UWGA-1070 24 0.107 ± 0.002 160 ± 10 1.5 CBM

VC4a UWGA-1071 29 0.134 ± 0.009 340 ± 20 0.9 CBM

VC4a UWGA-1072 36 0.156 ± 0.002 540 ± 30 0.7 CBM

VC4a UWGA-1073 42 0.182 ± 0.002 830 ± 40 0.5 CBM

VC5a 300250 6175500 UWGA-588 150 0.182 840 ± 40 1.8 CBM

VC5a UWGA-589 210 0.256 ± 0.007 2,030 ± 90 1.0 CBM

VC6a 299500 6174800 UWGA-626 365 0.348 ± 0.005 4,230 ± 190 0.9 CBM

VC7a 299100 6174700 UWGA-628 125 0.079 ± 0.003 40 ± 5 31.3 FPD

VC7a UWGA-629 255 0.132 ± 0.018 320 ± 10 8.0 FBD

VC8a 298863 6174310 UWGA-546 375 0.119 ± 0.004 230 ± 10 16.3 FPD

VC15a 301741 6181297 UWGA-826 50 0.089 ± 0.002 70 ± 5 7.1 FPD

VC20a 299300 6175600 UWGA-618 166 0.125 ± 0.004 270 ± 10 6.1 CBM

VC20a UWGA-619 234 0.289 ± 0.005 2,710 ± 120 0.9 CBM

VC20a UWGA-620 428 0.304 ± 0.004 3,070 ± 140 1.4 CBM

VC38a 303402 6180005 UWGA-1289 13 0.079 ± 0.030 40 ± 5 3.3 FPD

VC38a UWGA-1290 23 0.169 ± 0.002 680 ± 30 0.3 CBM

VC62a 298288 6174814 UWGA-1367 36 0.152 ± 0.001 510 ± 20 0.7 CBM

VC62a UWGA-1368 85 0.243 ± 0.003 1,780 ± 80 0.5 FPD

CBM Central basin mud facies, FPD fluvial pro-delta faciesa Sample previously reported in Sloss et al. (2006) to establish a Holocene chronostratigraphy and used here to compare pre- and post

European sedimentation rates

J Paleolimnol (2011) 46:561–577 569

123

low-energy depositional environment dominated by

the settling of fine-grained detritus from suspension

(Fig. 2). The relatively constant activity of 226Ra

down the core indicates one source of sediment (fine-

grained silty mud; Table 2). The data indicates that a

linear decrease in activity is present in the top 12 cm

of the core before reaching background levels for the

detection of excess 210Pb (Fig. 4a, b). The age/depth

profile indicates a relatively constant sedimentation

rate of 7.5 ± 0.5 mm/year for the top 12 cm of the

core which was deposited over the last 16 years

(Fig. 4a, b).

St Georges Basin: central basin (StGBPb)

A 25 cm core was collected from the central receiv-

ing basin of the St Georges Basin (Fig. 3) in a water

depth of 3 m in the vicinity of Sanctuary Point. This

region of the estuary represents a low-energy depo-

sitional environment dominated by the settling of

fine-grained detritus from suspension (Fig. 4c, d).

The age/depth profile indicates a relatively constant

sedimentation rate of 0.6 ± 0.3 mm/year for the top

8 cm which was deposited over the last 52 years

(Fig. 4c, d).

St Georges Basin: Erowal Bay (EbPb1)

A 30 cm core was collected from the bay in a water

depth of 80 cm (Fig. 3). The core was collected from

the pro-delta associated with the Worrowin Water-

way, an area within Erowal Bay that has a potential

for faster rates of sediment accumulation due to

adjacent extensive urban development (Fig. 3). The

plot of excess 210Pb indicates that sediments at a

depth of 30 cm in the core have not attained

background level, with excess 210Pb activity extend-

ing to a depth of 29.5 cm and displaying a linear

decrease in activity (Table 2; Fig. 4). The age/depth

profile indicates a relatively constant sedimentation

rate of 4.4 ± 0.9 mm/year for the top 30 cm depos-

ited over the last 65 years (Fig. 4e, f).

St Georges Basin: Erowal Bay (EbPb2)

A second 30 cm core was collected from Erowal Bay

in a water depth of 80 cm (Fig. 3). This core was

collected from the central basin of Erowal Bay away

from the pro-delta associated with Toomarong Creek

and the Worrowin Waterway (Fig. 3). The data for

samples above 20.5 cm represent a linear decrease in

excess 210Pb activity. The age/depth profile indicates

a relatively constant sedimentation rate of

1.4 ± 0.8 mm/year for the top 20.5 cm of the core

which was deposited over the last ca 147 years

(Fig. 4g, h).

Cesium 137

The 137Cs data for core samples from Lake Illawarra

suggest a sedimentation rate within both the Mullet

Creek and Macquarie Rivulet pro-delta facies of

approximately 4–5 mm/year over the last 50 year

(Table 4; Fig. 5). The core from Howards Bay

(MRD#2) did not provide a clear first detectable

appearance in 137Cs activity and these data, therefore,

can only be used to indicate a minimum accumulation

rate of at least 1.5 mm/year.

Table 4 137Cs (Bq/kg) results for cores MRD#2; MRD#3 and

LI-41 collected from Lake Illawarra

Core code Depth Cs-137 activity

MRD#2 0–2 0.18

2–4 0.23

5–6 0.23

6–7 0.17

7–8 0.11

8–9 0.14

MRD#3 0–2 0.2117

5–6 0.2615

7–8 0.2263

11–12 0.2472

13–14 0.1637

17–18 0.2032

20–21 0.1153

25–26 0.011

LI-41 1 0.3281

4.5 0.3409

8 0.5473

11 0.5619

14 0.369

18 0.1287

22 0.1328

26 0.0001

33 0.0001

570 J Paleolimnol (2011) 46:561–577

123

Amino acid racemisation

Aspartic acid racemisation derived ages for sediment

cores from Lake Illawarra presented in this study

(Table 3) have been supplemented by aspartic acid

data previously reported in Sloss et al. (2004a, b).

However, in this study sample ages have been

calculated from the new and previously reported data

using more accurate calibration curves presented by

Sloss et al. (2006). The aspartic acid ages presented

in this study are for the uppermost, relatively recent

sedimentary succession preserved in the central basin

and fluvial pro-delta depositional environments. Ages

range from 40 cal year BP to mid Holocene

(Table 3). The Holocene geomorphological evolution

of the estuary is examined in detail in Sloss et al.

(2006), while in this study the data are used to

compare pre- and post-European sedimentation rates.

The results also include the first application of the

amino acid racemisation reaction observed in the

gastropod B. australis as a geochonological control

(Table 5).

B. australis is an epifaunal gastropod that inhabits

low-energy back-barrier mud and sand-flat environ-

ments. The preservation of B. australis within the

sediment profile can be assumed to be contempora-

neous with the time of sediment deposition due to its

epifaunal nature. This has significant benefits over the

use of A. trapezia and N. trigonella which are semi-

infunal bivalves that can live several centimetres

below the sediment water interface. To determine the

rate of the racemisation reaction in B. australis, and

thus a calibration curve, a time-series experiment was

conducted. Radiocarbon ages necessary for the

experiment were obtained for fossil B. australis in

which the degree of aspartic acid racemisation was

also measured, and aspartic acid racemisation was

measured in shells obtained from living samples. The

radiocarbon ages range from 1,670 ± 190 cal year

BP (OZH-292) to 5,370 ± 200 cal year BP (OZH-

287) and the corresponding aspartic acid D/L ratios

range from 0.274 ± 0.004 to 0.574 ± 0.004

(Table 5). Preliminary results indicate the racemisa-

tion reaction follows an apparent parabolic model for

this gastropod, but at a significantly faster rate than

those previously reported for the bivalves A. trapezia

and N. trigonella (Sloss et al. 2004b, 2006; Table 5;

Figs. 6, 7).

The much faster rate of aspartic acid racemisation

observed in B. australis makes this mollusc well-

suited for dating geologically young (\300 year)

deposits and potentially provides a framework with

which to quantify recent sedimentation rates in

estuarine environments. However, these results are

based on a limited data set (n = 5) and must be

regarded as a first approximation of the aspartic acid

kinetic trend observed in B. australis (Figs. 6, 7).

0

5

10

15

20

25

30

0 0.1 0.2 0.3 0.4 0.5

Core MRD#2

Core MRD#3

Core LI-41

137Cs activity Bq/kg C

ore

dept

h (c

m)

Fig. 5 Plot of 137Cs activity down core in cores MRD#2;

MRD#3 and LI-41 (for core locations see Fig. 2)

Table 5 Radiocarbon derived ages and aspartic acidartic acid D/L ratios (total acid hydrolysate) obtained on Holocene specimens of

Batillaria australis from various estuaries on the NSW south coast

Radiocarbon

laboratory code

Laboratory code Location Avg. aspartic

acid D/LRadiocarbon age

(uncorrected)

Radiocarbon age

(cal year BP)

OZH-290 UWGA-1500 Lake Illawarra 0.472 ± 0.007 3,360 ± 40 3,200 ± 210

OZH-296 UWGA-1510 Lake Wollumboola 0.485 ± 0.014 3,000 ± 40 2,770 ± 200

OZH-287 UWGA-1471 Lake Wollumboola 0.574 ± 0.004 5,020 ± 50 5,370 ± 200

OZH-292 UWGA-1502 St Georges Basin 0.274 ± 0.004 2,090 ± 40 1,670 ± 190

OZH-293 UWGA-1503 Lake Burrill 0.711 ± 0.007 4,600 ± 50 4,790 ± 240

J Paleolimnol (2011) 46:561–577 571

123

Further radiocarbon analyses and simulated ageing

(heating) experiments are required to more accurately

model the kinetic trend of aspartic acid in

B. australis.

Discussion

Northern Lake Illawarra

An articulated N. trigonella from a core depth of

65 cm in the pro-delta of Mullet Creek, in the

northern part of Lake Illawarra, gave an aspartic

acid derived age of 190 ± 10 year, indicating a

sedimentation rate in the pro-delta environment of

approximately 3.4 mm/year over the last 200 years

(VC3; Table 3). This is a major increase compared

with sedimentation rates associated with the under-

lying estuarine mud that accumulated at a rate of

\1 mm/year over the previous 2,500 years (Sloss

et al. 2005).

Similar trends in sedimentation rates were also

identified in the Hooka Creek bay-head delta

(Fig. 2b) where an aspartic acid racemisation-derived

age of 70 ± 5 year was obtained on an articulated

N. trigonella at a depth of 50 cm, indicating a

sedimentation rate of 7.1 mm/year (VC15; Table 3).137Cs data obtained from the northern region of the

lagoon indicate that farther into the central basin the

sedimentation rate decreases to 3 mm/year for the

last 47 years (LI-41; Fig. 3, 5; Sloss et al. 2004a). A

similar decrease is identified towards the central

basin in the northern area of the lagoon were an

aspartic acid derived age of 40 ± 5 year on an

articulated N. trigonella at a depth of 13 cm indicates

a sedimentation rate of 3.3 mm/year (VC38;

Table 3). Accumulation rates of 3–5 mm/year were

also obtained in Griffins Bay in the northeastern

portion of the lagoon by Chenhall et al. (1995) using

ash and metal profiles.

In the Mullet and Hooka Creek delta regions in

northern Lake Illawarra sedimentation rates of

[5 mm/year were determined proximal to the delta

front. This rate decreases to 3–5 mm/year in the pro-

delta region and further decrease to a rate of between

1 and 4.5 mm/year in the central basin (Table 3;

Fig. 2). These sedimentation rates in the central

basin, while significantly less than rates in the delta

front and pro-delta are higher than the sedimentation

rates for the underlying pre-European estuarine mud

with an average rate of 0.6 mm/year (Table 3; Fig. 2;

Sloss et al. 2004a).

Macquarie Rivulet delta

Lithostratigraphic evidence indicates that the pro-

grading fluvial sands in this delta lie directly over

cohesive estuarine mud of mid Holocene age. The

rate of delta progradation was determined by Sloss

et al. (2005, 2006), based on a combination of

radiocarbon and aspartic acid racemisation-derived

ages, and indicate that most of the delta is a relatively

recent deposit, with the majority of the 1.3 km

0.8

Radiocarbon age (cal yr BP)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

2000 3000 4000 5000 6000 7000 8000 9000

Asp

artic

aci

d D

/L r

atio

A. trapezia

N. trigonella

B. australis

0 1000

Fig. 6 Comparison of the different rates of aspartic acid

racemisation observed in radiocarbon dated A. trapezia,

N. trigonella and B. australis. Racemisation rates for

A. trapezia and N. trigonella established from Sloss et al.

(Sloss et al. 2004a, b; 2006)

B. australis0.8

y = 0.0079x + 0.049

R 2 = 0.90

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 10 20 30 40 50 60 70 80

Square root of radiocarbon age (cal yr BP)

Fig. 7 Aspartic acid D/L ratio and square-root of the

equivalent radiocarbon ages obtained on specimens of the

estuarine gastropod B. australis

572 J Paleolimnol (2011) 46:561–577

123

extension into the lagoon occurring over the last

300 years (Fig. 2c). Recent delta progradation is also

supported by aspartic racemisation derived ages of

320 ± 10 year (VC7) and 230 ± 10 year (VC8) for

in situ specimens of articulated N. trigonella col-

lected from the pro-delta mud facies that sits

immediately beneath the fluvial bay-head delta

(Table 3).

Modern sedimentation rates proximal to the Mac-

quarie Rivulet pro-delta were also determined using a

combination of aspartic acid racemisation derived

ages and a 137Cs profile. Aspartic acid data for

N. trigonella indicate that post-European settlement

sedimentation rates close to the delta front can be as

high as 31.3–16.3 mm/year (VC7 and VC8; Table 3).

Previously reported 137Cs data for the active delta

margin deposits support these very high estimates and

gave an accumulation rate of at least 16 mm/year

(Chenhall et al. 1995). The 137Cs profile (MRD#3;

Figs. 2, 5; Table 4) obtained from Koona Bay, just

south of the active distributary, indicates a sedimen-

tation rate of approximately 4–5 mm/year. However,

the 137Cs profile in Haywards Bay (MRD#2; Figs. 2,

5), to the north of the main Macquarie Rivulet delta,

is incomplete and provides only an estimate of the

minimum modern sedimentation rate ([1.5 mm/year;

Figs. 2, 5). Sedimentation rates at the active pro-delta

front and farther into the central basin have also been

determined using aspartic acid racemisation derived

ages from in situ N. trigonella. These rates range

from 3.2 mm/year (VC7) in the pro-delta front to

1.8 mm/year in the central basin (VC5; Table 3).

The Lake Illawarra central mud basin facies

This facies is composed of very fine-grained grey/

black estuarine silty clay (avg. size = 0.005 mm),

with a high concentration of organic detritus charac-

teristic of anoxic environments. The silty mud

comprises fine-grained terrigenous detritus supplied

from the freshwater streams entering the estuary. The

fine-grained detritus would have rapidly flocculated

in the brackish to fully saline environment within the

estuaries (as it does at present) and not been flushed

from the system by circulating tidal currents.

N. trigonella dominate these strata and occur as a

life assemblage of dense shell beds, with abundant

articulated shells that indicate in situ preservation.

The relatively uninterrupted sediment supply and

minimal surface mixing makes the central basin mud

facies an ideal site to measure recent sedimentation.

The age/depth plot based on the excess 210Pb

profile indicates a higher sedimentation rate for the

top 12 cm of core LkPb2 (Fig. 4). This rate was

calculated to be 7.5 mm/year and indicates that the

top 12 cm was deposited over the last ca 16 years.

This rate of sedimentation is higher than the rate

established by amino acid racemisation dating on

N. trigonella from the central basin (between 2.0 and

4.5 mm/year; VC4, LkPb1; LkPb2; VC38; Table 3).

However, age determinations on fossil shells of this

bivalve represent a less precise age due to the semi-

infaunal habitat of the species. Sedimentation rates

may also be higher than indicated, as sediment that

the molluscs are preserved in may be older than the

fossil. However, as the molluscs used in this study are

epifaunal, this age discrepancy between sediment and

in situ fossils is regarded as minor. Despite a possible

underestimated sedimentation rate, the aspartic acid

determined sedimentation rates indicate a significant

increase in sedimentation within Lake Illawarra

compared to the underlying Holocene central basin

mud facies which accumulated at an average rate of

ca. 0.4 mm/year (Sloss et al. 2004a; Table 3).

St Georges Basin central basin mud facies

The 25 cm core collected from the central lagoon of

St Georges Basin (StGBPb1; Fig. 3; Table 2) pro-

vided excess 210Pb data for only the top 8 cm. The

age/depth profile indicates a relatively constant

sedimentation rate of 0.62 ± 0.25 mm/year over

approximately the last 52 years. A similar sedimen-

tation rate 0.5 mm/year is indicated by the aspartic

acid racemisation-derived age for B. australis at a

depth of 5 cm in the central basin (110 ± 5 year;

SGB4-H; Fig. 3; Table 6). This rate is the same as the

pre-European sedimentation rate based on aspartic

acid data (Table 6) and excess 210Pb data (Fig. 4);

and is similar to rates measured in the mid to late

Holocene estuarine muds in Lake Illawarra (0.4 mm/

year; Table 3). These data show that sedimentation in

this part of St Georges Basin has been relatively

constant over the last 500 years and probably since

the mid Holocene.

J Paleolimnol (2011) 46:561–577 573

123

Erowal Bay

Two additional cores from this sheltered embayment

within the northeastern reach of St Georges Basin

were analysed for 210Pb (Fig. 3). The 210Pb core

collected from the pro-delta associated with Worro-

win Waterway (EbPb1; Fig. 3) indicates that there

has been a relatively constant accumulation rate of

4.4 ± 0.9 mm/year for at least the top 30 cm of the

sediment profile (Fig. 4). This is significantly higher

than the modern sedimentation rate in the central

lagoon of St Georges Basin. The high accumulation

rate and source of sediment in Erowal Bay is most

likely associated with urban development on the

margin of the bay and within the catchment of the

Worrowin Waterway.

The 210Pb core from the central region of Erowal

Bay was collected in a low-energy environment away

from the deltas associated with Toomarong Creek and

the Worrowin Waterway (EbPb2; Fig. 3). Data

obtained from this core suggest a relatively constant

sedimentation rate of 1.4 ± 0.8 mm/year for the top

20.5 cm of the sediment profile (Fig. 4). This is similar

to the sedimentation rate observed for the underlying

central basin mud facies where an articulated specimen

of A. trapezia at a depth of 181 cm yielded a

radiocarbon age of 1,190 ± 190 cal year BP, indicat-

ing a sedimentation rate of 1.5 mm/year (Sloss et al.

2006). Overall, data for the central basin environment

of Erowal Bay indicate a relatively constant rate of

sedimentation, while there has been rapid modern

sedimentation within Worrowin Waterway.

Comparison between Lake Illawarra and St

Georges Basin

Sedimentation in coastal lagoons is part of the natural

infilling cycle for coastal valleys drowned by the

post-glacial sea level rise to form barrier estuaries

(Dalrymple et al. 1992; Roy et al. 2001; Heap et al.

2004; Sloss et al. 2006). The rate of infilling depends

on the size and nature of the river catchments feeding

into the lagoons together with the depth and size of

the receiving basin in which the sediment accumu-

lates and the prevailing marine environment (Heap

et al. 2004). Lake Illawarra and St Georges Basin

have similar climates and marine environments,

similar lagoon areas, similar ratios of catchment area

to lagoon area and receive discharge from two

streams that drain the catchments. However, even

though both catchments would have had similar

forest cover (Mills and Jakeman 1995), the measured

sedimentation rates under natural conditions prior to

European settlement are approximately double in

Lake Illawarra. The difference in sedimentation rate

can at least in part be accounted for by differences in

elevation of the catchment area. Lake Illawarra is

bounded by a higher and steeper catchment and

closer escarpment than St Georges Basin. As a

consequence, the Lake Illawarra catchment has

higher runoff rates and volumes caused by the steeper

stream gradients and heavy rainfall events related to

orographic uplift of low-pressure cells (Reinfelds and

Nanson 2001). Rates of erosion and sediment trans-

port are, therefore, likely to be much higher in the

Lake Illawarra catchment.

Changes in land use patterns since the arrival of

European settlers have been more pronounced in the

Illawarra region, with extensive land clearing for

agriculture and later by urban and industrial devel-

opment. These changes have caused a considerable

increase in modern sediment accumulation rates in

Lake Illawarra whereby it now has a sedimentation

rate 6–10 times that of St Georges Basin. In contrast,

the St Georges Basin catchment retains a high

proportion (*80%) of forested catchment (Haese

et al. 2007).

Table 6 Aspartic acid racemisation-derived ages on B. australis from St Georges Basin on the NSW south coast

Core

code

UTM

easting

UTM

northing

Sample UWGA

laboratory code

Sample core

depth (cm)

Aspartic acid

avg. D/LAspartic acid

derived age

Cumulative sedimentation

rate (mm/year)

SGB4-H 285156 6108449 UWGA-1460 5 0.133 ± 0.002 110 ± 5 0.5

UWGA-1461 22 0.222 ± 0.002 480 ± 20 0.5

UWGA-1462 27.5 0.229 ± 0.002 520 ± 20 0.5

UWGA-1464 51 0.322 ± 0.004 1190 ± 50 0.4

UWGA-1465 59 0.335 ± 0.003 1310 ± 60 0.5

574 J Paleolimnol (2011) 46:561–577

123

The sedimentation rates determined for Lake

Illawarra and St Georges Basin in this study

complement data from previous studies in these and

other similar estuarine systems of the southeastern

coast of Australia. For example, sedimentation rates

for the pre-European central mud basin in Lake

Illawarra based on radiocarbon ages were determined

to be \1 mm/year, whereas post-European sedimen-

tation rates around the margins of the lagoon are

generally[5 mm/year (Chenhall et al. 2001). Using a

larger data base, Jones and Chenhall (2001) reported

pre-European sedimentation rates for the mud basin

ranging from 1.2 to 2 mm/year. The addition of

anthropogenic detritus into Lake Illawarra can also be

used to determine recent sedimentation rates when

the date of first released of the pollutant is known.

Trace metals from smelting and manufacturing and

fly ash from coal-burning power stations are cases in

point. In Lake Illawarra increases in trace element

abundance, especially in the northern and central

parts of the lagoon, show sedimentation rates of

3–5 mm/year over the past 70–90 years (Payne et al.

1997; Chenhall et al. 2001). Likewise fly ash

concentrations in the western and southwestern

portions of the lagoon indicate accumulation rates

of 11 to [16 mm/year associated with the extension

of Macquarie Rivulet delta as a result of increased

agriculture and urbanisation (Payne et al. 1997;

Chenhall et al. 1995, 2001).

Sediment has accumulated in the prodelta deposi-

tional environment near Wandandian Creek delta in

the western reach of St Georges Basin at a rate of

0.5 mm/year over the past 1,000 years with only a

minor increase to 0.6 mm/year (210Pb) over the past

20 years (Hopley and Jones 2006). The relatively low

accumulation rates probably reflect the influence of

extensive forest cover in the catchment and the

relatively large surface area of the basin over which

sedimentation may occur. Sedimentation rates

increase to about 3 mm/year closer to the active

delta front.

The results from this study indicate that the

uppermost portions of most sediment cores in all

these coastal lagoons show an increased rate of

sedimentation that is partly related to lower compac-

tion of the upper part of the sediment column and

partly a result of increased sediment runoff from the

catchments caused by recent land use changes.

Sedimentation can also vary spatially, especially

where there is a significant fluvial input to the

estuary. For example, sedimentation rates closer to

fluvial deltas in Lake Illawarra range between 5.1 and

[16 mm/year, while sedimentation rates within the

central basin are up to 7 mm/year. However, sedi-

ments deposited in the central basin comprise thixo-

tropic estuarine mud and have not undergone

significant compaction and dewatering over the last

two to three decades. This means that the apparent

recent sedimentation rates in all the central basins of

coastal lagoons are significantly higher than the long-

term average. However, taking into account likely

differential sediment compaction can provide a more

realistic comparison between the modern and pre-

European periods. Assuming a compaction rate of

5–25% (based on compaction rates (see Sloss et al.

2005, 2006) in the pre-European to late Holocene

sediment provides conservative modern sedimenta-

tion rates in these lagoons that range between 2 and

4.5 mm/year for the central basin estuarine muds

(Sloss 2005). This is still a significant increase in

sedimentation compared to the rates measured in the

pre-European deposits (0.4–0.8 mm/year) that are

less than 200 years old in this region.

In contrast, sedimentation rates in the central basin

of St Georges Basin appear to have remained very

similar to the pre-European rate. This may be in part

due to the largely intact native vegetation of the

catchment. However, in the Erowal Bay reach of St

Georges Basin sedimentation rates are up to 4.4 mm/

year compared to 0.5 mm in the pre-European period

(Table 3; Sloss et al. 2004a, b, 2006). This sedimen-

tation rate is similar to modern rates measured in

Lake Illawarra and is attributed to recent expansion

of the urban fringe of the northern bay.

Conclusions

The impacts of modern changes in catchment land use

on estuary sedimentation can be obtained from sedi-

ment cores dated using a range of methods. In this study

these data provide a chronostratigraphic framework for

modern estuary sedimentary deposits in southeastern

Australia that enable important comparisons to be

made of sedimentation rates over the last 100 years

with rates that occurred prior to European settlement.

Results indicate that in Lake Illawarra, which has a

heavily modified catchment, sedimentation rates close

J Paleolimnol (2011) 46:561–577 575

123

to fluvial deltas can be in excess of 16 mm/year, and

between 2 and 4 mm/year in the adjacent central basin,

approximately an order of magnitude greater than the

pre-European rates. Accordingly, results from this

study show that for this estuary, clearance of native

vegetation (forest) in the catchment, urban expansion

and development of heavy industry are factors linked

to accelerated sedimentation and more rapid fluvial

delta progradation.

In contrast, at St Georges Basin, where the

catchment retains approximately 80% of the native

forest cover, sedimentation rates in the central basin

appear to have remained close to those prior to

European settlement. However, sedimentation rates

in the urbanized margin of St Georges Basin are

relatively high (up to 4.4 mm/year). This rapid

modern sedimentation in the margin of the bay has

been detected in several other estuaries in the region,

including in central basins and bay-head deltas, and

appears proportional to the degree of land-use change

in the respective catchment areas.

Acknowledgments Financial and field work support for this

project was provided by the School of Earth and

Environmental Sciences and GeoQuest at the University of

Wollongong, an ARC Linkage Grant (LP0347365) in

conjunction with Shoalhaven City Council, an Australian

Institute of Nuclear Science and Engineering postgraduate

award and research award (02/069P). The 210Pb and 137Cs

analyses were conducted at the ANSTO Lucas Heights

Environmental Laboratory with the assistance of Jennifer

Harrison and Atun Zawadzki. The amino acid racemisation

measurements were undertaken in the University of

Wollongong AAR laboratory. This paper is a contribution to

IGCP Project 588 ‘‘Preparing for Coastal Change’’ and INQUA

working group on ‘‘Coastal and Marine Processes’’.

References

Bradshaw BE (1987) St Georges Basin—morphology and late

quaternary deposits. BSc Honours thesis, University of

Sydney, Sydney (unpublished)

Bradshaw BE (1993) Late quaternary evolution of the St

Georges Basin barrier—estuary system. In: Thomas MC

(ed) Catchments and coasts in eastern Australia. Depart-

ment of Geography, University of Sydney, Research

Monograph 5, Sydney, pp 60–71

Brooke B (2003) The role of sedimentological information in

estuary management. Proceedings of coast to coast

2002—‘‘source to sea’’, Tweed Heads, pp 31–34

Chenhall BE, Batley GE, Yassini I, Depers AM, Jones BG

(1994) Ash distribution and metal contents of Lake

Illawarra bottom sediments. Aust J Mar Freshw Res

45:977–992

Chenhall BE, Yassini I, Depers AM, Caitcheon G, Jones BG,

Batley GE, Ohmsen GS (1995) Anthropogenic marker

evidence for accelerated sedimentation in Lake Illawarra,

New South Wales, Australia. Environ Geol 26:124–135

Chenhall BE, Jones BG, Depers AM (2001) Trace-metal pol-

lution and sedimentation in coastal lagoons: an example

from Lake Illawarra, New South Wales, Australia. In:

Gostin VA (ed) Gondwana to greenhouse: Australian

environmental geoscience. Geological society of Austra-

lian special publication 21, pp 227–233

Chenhall BE, Jones BG, Sloss CR, O’Donnell M, Payne M,

Murrie M, Garnett D, Waldron H (2004) Trace metals in

sediments from Lake Illawarra, New South Wales, Aus-

tralia. Wetlands (Australia) 21:198–208

Costanza R, d’Arge R, de Groot R, Farber S, Grasso M,

Hannon B, Limburg K, Naeem S, O’Neill R, Paruelo J,

Raskin R, Sutton P, Van den Belt M (1997) The value of

the world’s ecosystem services and natural capital. Nature

387:253–260

Dalrymple RW, Zaitlin BA, Boyd R (1992) Estuarine facies

models; conceptual basis and stratigraphic implications.

J Sediment Petrol 62:1130–1146

Gillespie R (1977) Sydney university natural radiocarbon

measurements IV. Radiocarbon 19:101–110

Gillespie R, Polach HA (1979) The suitability of marine shells

for radiocarbon dating of Australian prehistory. In: Berger

R, Suess H (eds) Proceedings of the 9th international

conference on radiocarbon. University of California Press,

Los Angeles, pp 404–421

Goodfriend GA (1991) Patterns of racemization and epimer-

ization of amino acids in land snail shells over the course

of the Holocene. Geoch Cosmoch Acta 55:293–302

Goodfriend GA (1992) Rapid racemization of aspartic acid in

mollusc shells and potential for dating over recent cen-

turies. Nature 357:399–401

Goodfriend GA, Stanley DJ (1996) Reworking and disconti-

nuities in Holocene sedimentation in the Nile delta: doc-

umentation from amino acid racemization and stable

isotopes in mollusk shell. Mar Geol 129:271–283

Haese RR, Murray EJ, Smith CS, Smith J, Clementson L,

Heggie DT (2007) Diatoms control nutrient cycles in a

temperate, wave-dominated estuary (southeast Australia).

Limnol Oceanogr 52:2686–2700

Hagan J, Wells A (1997) A history of Wollongong. University

of Wollongong Press, Wollongong, pp 23–71

Haworth RJ, Gale SJ, Short SA, Heijnis H (1999) Land use and

lake sedimentation on the New England tablelands of

New South Wales, Australia. Aust Geogr 30:51–73

Heap AD, Bryce S, Ryan DA (2004) Facies evolution of

Holocene estuaries and deltas: a large-sample statistical

study from Australia. Sediment Geol 168:1–17

Hopley CA, Jones BG (2006) Holocene stratigraphic and

morphological evolution of the Wandandian Creek delta,

St Georges Basin, New South Wales. Aust J Earth Sci

53:991–1000

Hopley CA, Jones BG, Puotinen M (2007) Assessing the recent

(1834–2002) morphological evolution of a rapidly pro-

grading delta within a GIS framework: Macquarie Rivulet

576 J Paleolimnol (2011) 46:561–577

123

delta, Lake Illawarra, New South Wales. Aust J Earth Sci

54:1047–1056

Jones BG, Chenhall BE (2001) Lagoonal and estuarine sedi-

mentation during the past 200 years. In: Heijnis H, Harle

K (eds) Archives of human impact of the last 200 years.

Australian Institute for Nuclear Science and Engineering

Workshop, Lucas Heights, pp 42–46

Jones BG, Eliot IG, Depers AM (1976) Sedimentation in Lake

Illawarra. In: Lake Illawarra environmental assessment

project, Wollongong City Council, pp 20–40, 147–148

Krishnaswamy S, Lal D, Martin JM, Meybeck M (1971)

Geochronology of lake sediments. Earth Planet Sci Lett

11:407–414

Leslie C, Hancock GJ (2008) Estimating the date correspond-

ing to the horizon of the first detection of 137Cs and

239 ? 240Pu in sediment cores. J Environ Radioact

99:483–490

Livens FR, Rimmer DL (1988) Pysico-chemical controls on

artificial radionuclides in soil. Soil Use Manag 4:63–69

Miller GH, Brigham-Grette J (1989) Amino acid geochronol-

ogy: resolution and precision in carbonate fossils. Quat Int

1:111–128

Miller GH, Hare PE (1980) Amino acid geochronology:

integrity of the carbonate matrix and potential of mol-

luscan fossils. In: Hare PE, Hoeing TC, King K (eds)

Biochemistry of amino acids: selected papers. Wiley, New

York, pp 415–451

Mills K, Jakeman J (1995) Rainforests of the Illawarra District.

Coachwood Publishing, Jamberoo

Murray-Wallace CV (1993) A review of the application of the

amino acid racemisation reaction to archaeological dating.

Artefact 16:19–26

Murray-Wallace CV, Kimber RWL (1987) Evaluation of the

amino acid racemization reaction in studies of quaternary

marine sediments in South Australia. Aust J Earth Sci

34:279–292

Payne M, Chenhall BE, Murrie M, Jones BG (1997) Spatial

variation of sediment-bound zinc, lead, copper and

rubidium in Lake Illawarra, a coastal lagoon in eastern

Australia. J Coast Res 13:1181–1191

Reinfelds I, Nanson GC (2001) Torrents of terror: magnitude,

frequency and impact of major storms and floods, Illa-

warra, New South Wales. Aust Geogr Stud 39:335–352

Robinson J (2001) The economic value of Australia’s estuar-

ies—a scoping study, OzCoasts. http://www.ozcoasts.org.

au/pdf/CRC/economic_value_estuaries.pdf

Roy PS, Peat C (1975) Bathymetry and bottom sediments of

Lake Illawarra. Geol Surv NSW Rec 17:65–79

Roy PS, Williams RJ, Jones AR, Yassini I, Gibbs PJ, Coates B,

West RJ, Scanes PR, Hudson JP, Nichol S (2001) Struc-

ture and function of south-east Australian estuaries. Estuar

Coast Shelf Sci 53:351–384

Sloss CR (2005) Holocene sea-level change and the aminos-

tratigraphy of wave-dominated barrier estuaries on the

southeast coast of Australia. Unpublished PhD thesis,

University of Wollongong. http://ro.uow.edu.au/theses/

447/

Sloss CR, Jones BG, Murray-Wallace CV, Chenhall BE

(2004a) Recent sedimentation and geomorphological

changes, Lake Illawarra, NSW, Australia. Wetlands

(Aust) 21:73–83

Sloss CR, Murray-Wallace CV, Jones BG, Wallin T (2004b)

Aspartic acid racemisation dating of mid-Holocene to

recent estuarine sedimentation in New South Wales,

Australia: a pilot study. Mar Geol 212:45–59

Sloss CR, Jones BG, Murray-Wallace CV, McClennen CE

(2005) Holocene sea level fluctuations and the sedimen-

tary evolution of a barrier estuary: Lake Illawarra, New

South Wales, Australia. J Coast Res 21:943–959

Sloss CR, Murray-Wallace CV, Jones BG (2006) Aminostra-

tigraphy of two Holocene wave-dominated barrier estu-

aries in southeastern Australia. J Coastal Res 22:113–136

Sloss CR, Murray-Wallace CV, Jones BG (2007) Holecene

sea-level change on the southeast coast of Australia: a

review. Holocene 17:1001–1016

Smith JN (2001) Why should we believe 210Pb sediment

geochronologies? J Environ Radioact 55:121–123

Stuiver M, Reimer PJ (1993) Extended 14C data base and

revised CALIB 3.0 14C calibration program. Radiocarbon

35:215–230

Stuiver M, Reimer PJ, Braziunas TF (1998a) High-precision

radiocarbon age calibration for terrestrial and marine

samples. Radiocarbon 40:1127–1151

Stuiver M, Reimer PJ, Bard E, Beck JW, Burr GS, Hughen KA,

Kromer B, McCormac FG, Plicht J, Spurk M (1998b)

INTCAL98 Radiocarbon age calibration, 24,000–0 cal

BP. Radiocarbon 40:1127–1151

Umitsu M, Buman M, Kawase K, Woodroffe CD (2001)

Holocene palaeoecology and formation of the Shoalhaven

River deltaic-estuarine plains, southeast Australia. Holo-

cene 11:407–418

Walling DE, He Q (1992) Interpretation of caesium-137 pro-

files in lacustrine and other sediments: the role of catch-

ment-derived inputs. Hydrobiologia 235/236:219–230

Walling DE, He Q (1997) Use of fallout 137Cs in investiga-

tions of overbank sediment deposits on river floodplains.

Cantena 29:263–282

Wehmiller JF, Miller G (2000) Aminostratigraphic dating

methods in Quaternary geology. In: Moller JS, Sowere

JM, Lettis WR (eds) Quaternary geochronology: methods

and applications. American Geophysical Union, Wash-

ington, DC, pp 187–222

J Paleolimnol (2011) 46:561–577 577

123